It is known that certain oil/gas wells produce from low pressure formations require artificial lift such as downhole pumping in order to bring the oil/gas to the surface for recovery. It is also necessary to use downhole pumping equipment in some oil/gas wells which have become low pressure as a result of the formation being somewhat expended. Typically, such low pressure wells utilize downhole pumping units for such artificial lift, sometimes referred to as "sucker rod" pumps to pump out the oil and gas from the formation. The sucker rod pump is mounted downhole in the area of the production zone near the end of production tubing which extends to the surface. The sucker rod pump mounted near the end of the production tubing is driven by a sucker rod which extends to and is driven by a surface pumping unit. Typically, the sucker rod pumps are two cycle pumps wherein fluid is removed upwardly through the tubing during the upstroke and the downstroke is a return of the lifting valve and fluid carrying piston to the bottom of its stroke.
In such a low pressure oil well which also contains gas, the sucker rod pump also brings to the surface the gas as well as oil. However, the presence of the gas which tends to come out of the oil/gas mixture as it leaves the formation and enters the borehole, can cause operating problems to the sucker rod pump. In such wells, gas can become trapped in the pump chamber causing a loss of efficiency and even a locking of the sucker rod piston, which can cause damage to the sucker rod and to the pumping unit itself. Gas lock is such a common phenomenon in sucker rod pumps that many wells cannot be produced because they contain too much gas.
Efforts have been made to separate out the gas from the oil/gas mixture coming out of the production zone and entering into the sucker rod pump. For example, U.S. Pat. No. 4,074,763 discloses a tool to be mounted near the end of the production string utilizing a series of concentric conduits for separating gas out of the oil/gas mixture utilizing centrifugal force. U.S. Pat. No. 4,074,763 requires that the oil/gas mixture travel initially downwardly with the separated oil reversing direction for removal.